This invention relates to a method of making a wound core for an electric transformer and, more particularly, relates to a method of this type in which a plurality of sheets primarily of magnetic steel are wound in superposed relationship about an arbor. The invention is also concerned with the core resulting from this method.
The method of this invention is preferably practiced with a high-speed machine that winds the sheets in rapid succession about the arbor, building up an annulus of gradually increasing diameter. When the required number of sheets have been wound in superposed relationship about the arbor, the resulting annulus is removed from the arbor and subjected to further processing, soon to be described.
A problem that is often encountered in practicing a method of the above type is that the sheets may have a tendency to "telescope" as they are wound about the arbor. The term "telescope", as used herein, denotes the tendency of the trailing edge of the sheet to become laterally displaced from the leading edge during the winding operation. The direction of the telescoping is the direction, considered axially of the arbor, that the trailing edge is displaced from the leading edge after the sheet is so wound. The magnitude of such displacement is referred to herein as the amount of telescoping. For various reasons, soon to be explained, telescoping, if it exceeds a predetermined amount, is highly objectionable.
Various solutions have been proposed for correcting the telescoping action and/or its results. One solution has been to place one side face of the finished annulus on a flat horizontal surface and to gently hammer the opposite side face of the annulus in such locations as to force the protruding telescoping sheets back into approximate edge-alignment with the other sheets. Thereafter, the side faces are placed between two planar members, and these planar members are pressed together to further improve the alignment of the edges of the sheets.
This approach works reasonably well if the sheets are relatively thick, e.g., 11 mils, and thus can usually withstand the above-described hammering and pressing without damage. But there is a growing movement in the industry to shift to thinner and thinner sheets, and such sheets are much more susceptible to being damaged by such hammering and pressing.
It is to be noted that the greater the amount of telescoping, the more susceptible the sheets are to being damaged by the above-described hammering or pressing since the greater the sheets protrude at their lateral edges, the less support they have in this region and the more easily deformed they are by edge-applied forces.
Other solutions proposed for the telescoping problem have been aimed at preventing the occurrence of substantial telescoping. One such proposed solution has involved feeding sheets onto the arbor so that their center lines are slightly angularly displaced from a reference plane perpendicular to the arbor axis. This approach is awkward and has not been very effective in limiting telescoping to the desired extent.
Still another proposed solution has been to provide means responsive to telescoping for angularly shifting the planar face of the sheets as they are fed onto the arbor. This approach likewise has not been very effective in limiting telescoping to the desired extent.